We propose to continue our ongoing studies at the University of Michigan Hospitals on the pathogenesis, epidemiology, diagnosis and treatment of Clostridium difficile colitis, a disease most often encountered as a side effect or complication of therapy with antibiotics or cancer chemotherapeutic agents. We will compare the responses to treatment of this disease with oral vancomycin, metronidazole or bacitracin, with special emphasis upon prevention and treatment of recurrences or relapses. We will evaluate the usefulness in our clinical and epidemiologic studies of two new research tools we have recently developed: 1) a selective culture medium containing taurocholate that is effective in detecting small numbers of spores of the organism, and 2) a bacteriophage-bacteriocin system for typing isolates. We will use our typing system in epidemiologic studies concerned with the sources, transmission, and prevention of transmission of the organism, especially in hospitals. We will determine the prevalence of antibodies to certain toxins of C. difficile in sera obtained from healthy and hospitalizaed humans of various ages, from patients with the disease at various times during or after the disease, and from patients who relapse.